Non-stoichiometry defects and radiation hardness of lead tungstate crystals PbWO4

Abstract

It has been stated many times that the formation of radiation infringements in P bW O 4 is to big extent stipulated by non-stoichiometry defects of the crystals, arising in the process of their growth and annealing. To refine the idea of characteristics of non-stoichiometry defects and their effect on the radiation hardness of P bW O 4 the current study is aimed at the melt composition infringements during its evaporation and at optical transmission of crystals obtained in these conditions after their irradiation ( 137 Cs source). In the optical transmission measurements along with traditional techniques a method "in situ" was used, which provided the measurements in fixed points of the spectrum (380, 470 and 535 nm) directly in the process of the irradiation. X-ray phase and fluorescence analysis of condensation products of vapours over P bW O 4 melt has found P bW O 4 phase in their content as well as compounds rich in lead, P bO, P b 2 W O 5 , with overall ratio P b/W = 3.2. Correspondingly the lack of lead and variations in the content of oxygen are pointed out as the major growth defects of non-stoichiometry of P bW O 4 crystals. The oxygen variations are determined by the partial oxygen pressure in the atmosphere of growth or annealing of the crystals.The obtained results were compared with known conceptions of P bW O 4 crystal colour centres. The possibilities of the formation of these centres accounting for the discovered loss of lead and oxygen exchange between the external medium and the crystal were considered.